Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds genuinely new behavior: UK-only coverage, a 25-credit cost, the fuzzy-vs-exact result caveat that a name match is a 'candidate set, NOT a portfolio', and the n_distinct_titles vs n_rows distinction.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with what it returns, then how to invoke it, then the interpretation caveat and cost. Every sentence carries distinct information with no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return-value documentation is unnecessary; the description still clarifies the two ambiguous response counts. Cost, region and match-mode caveats round out what an agent needs to call it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With 0% schema description coverage, the description must compensate, and it does for name (fuzzy substring) and company_number (exact match). The limit parameter is not described at all, so it does not fully cover the three parameters.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource with concrete scope: 'What the Land Registry shows for one proprietor: titles held, company status, country of incorporation, directors and PSCs.' This clearly distinguishes it from sibling tools like ownership_by_company or search_entities.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit when-to-use rule for the two lookup modes ('Give a company number for an EXACT match. A name is a fuzzy substring search') and warns how to interpret name-matched results. It does not name a specific alternative sibling tool, which keeps it just below full marks.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.